Siloxane-polyether copolymers may be linear, branched, hydrolyzable or nonhydrolyzable structures. U.S. Pat. Nos. 4,657,959 and 4,752,633 disclose their use as semipermanent hydrophilic additives in dental impressions.
Polydiorganosiloxane having terminal or pendant unsaturated hydrocarbon groups are known. Typical examples are the linear polydimethylsiloxanes having a vinyl group attached to the silicon atom at each terminus of the chains, and the linear polydimethylsiloxanes with vinyl groups randomly distributed on silicon atoms in the chains. Polysiloxane-polyether copolymers bearing terminal methacrylate groups impart durable hydrophilicity to the contact lens compositions of U.S. Pat. Nos. 4,259,467 and 4,260,725. Aoki, et al., Macromolecules, Rapid Communications, 18 (1997) 31-36, synthesized hydrolyzable siloxane-polyether copolymers of general formula, [(R'.sub.2 SiO)--(C.sub.2 H.sub.4 O).sub.7 ].sub.20-35, wherein R'=vinyl. While all of these functionalized polysiloxane-polyether copolymers can be reacted into polymer matrices or onto surfaces to improve hydrophilicity, water absorption, lubricity and/or adhesion, the reactions do not result in the formation of Si--C bonds between the matrix or substrate and the functionalized polysiloxane-polyether. Si--C bonds are desirable because they are strong and nonhydrolyzable.
U.S. Pat. No. 5,580,921 discloses storage-stable polysiloxane compositions which impart permanent hydrophilicity to addition cure dental impression compounds. Permanent hydrophilicity is provided by polysiloxane-polyether copolymers which have 10-400 silicon atoms per molecule, which contain unsaturated functionalities and which are free of noble metal catalysts. The copolymers become bound to the polysiloxane matrix by Si--C bonds during the curing step. Synthesis of the copolymers comprises the preparation of a distillable silane-polyether compound followed by its hydrolysis, condensation and equilibration with alkenyl siloxanes. The copolymer chain lengths are greater than 10 and are miscible with the .alpha., .omega.-divinylpolysiloxanes used in addition cure formulations. This feature facilitates storage stability of the two part formulations and avoids the need to use the copolymer as a separate component. However, the copolymers of long siloxane chain length do not afford the most rapid spreading of water and wetting of the cured polysiloxane surface.